• The elucidation of relationships between biodiversity and ecosystem processes has been
limited by the definition of metrics of biodiversity and their integration into
experimental design. Functional trait screening can strengthen the performance of these
designs.

• We suggest the use of Rao’s quadratic entropy to measure both functional diversity and
phylogenetic diversity of species mixtures proposed for an experimental design, and
demonstrate how they can provide complementary information.

• We also present an index assessing the statistical performance of these independent
variables in different experimental designs. Measurement of independent variables as
continuous vs. discrete variables reduces statistical performance, but improves the model
by quantifying species differences masked by group assignments.

• To illustrate these advances, we present an example from a tropical forest tree
community in which we screened 38 species for nine functional traits. The proposed
TropiDEP design is based on the relative orthogonality of two multivariate trait axes
defined using principal component analysis.

• We propose that independent variables describing functional diversity might be grouped
to calculate independent variables describing suites of different traits with potentially
different effects on particular ecosystem processes. In other systems these axes may
differ from those reported here, yet the methods of analysis integrating functional and
phylogenetic diversity into experimental design could be universal.